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Use PIC16f877A to turn on relay and magnetic valve.Why MCu hot?

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babboy12345

New Member
As tilte,when i turn on MCU,it can run the relay,and the relay on,then relay on the valve.But i face a very critical problems,MCU very hot.I'm using transistor as switch to turn on my relay!......Please help me....neary cry le
 

tresca

Member
lol.

I can understand if you dont have any sort of schematic software and if you use word, make it look good, you want help right ? Why should people have to look at a mess for you ?

And most relays have at least 4 connections. power(2) and contact(2).
 

babboy12345

New Member
ya,i really do not have any draw software.I can say that my relay work in good condition,and i connect all the 4 pins.Now i just scare is that got any current feedback to my MCU unit.
 

babboy12345

New Member
i hope this is clear enough to let you all to understand what i am doing.

1. MCU will feed 2.5v to base,then will turn on the transistor.
2. relay will turn on,and the coil will operated.
3. valve turn on

my problems are,when the circuit turn on the valve,the MCU will becum very hot,if i off the valve supply 240V,the relay stilll can switch on and off,bt MCU no get hot.
View attachment hahaha.doc
 

Sceadwian

Banned
You're going to have to post a much more detaile schematic, perferably something not done in MS paint, showing how you have your PIC wired.
 

Sceadwian

Banned
Sounds like you're measuring the voltage drop at the transistor base. Try it without the transistor there, you'll get 5V's.
 

Mikebits

Well-Known Member
Are you sure your supply has enough current drive? Verify your 5v stays 5v.
 

Mikebits

Well-Known Member
Sounds like you're measuring the voltage drop at the transistor base. Try it without the transistor there, you'll get 5V's.
It would be .7v at the base as oppossed to 2.5v
 
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babboy12345

New Member
before my 5v to MCU circuit,i got put a 10k resistor.Is that my MCU circuit must have more current?? But the way, why my relay and valve still can function,and cause the MCU very fast. If i just turn on relay,but the valve i off it,then my MCU will be fine........Please help me,3 more days i need to demonstration my project.
 

Mikebits

Well-Known Member
Last edited:

blueroomelectronics

Well-Known Member
See why it helps to draw schematics. Can't see how you could heat up a 16F877 with a 10K on VDD though. Do you have decoupling caps? Both VDD & VSS connected? Stable regulated 5V?
 
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